2-(Phenyl methyl thio)-3-pyridine carboxylic acid is a derivative of pyridine carboxylic acid having a wide range of commercial uses. Pyridine derivatives have, for many years, been investigated for use in the biological sciences like used as an intermediate for the preparation of various agrochemical preparations and in particular, as herbicides, which may be selective to corn.
Processes for producing 2-(Phenyl methyl thio)-3-pyridine carboxylic acid are known. The processes for producing 2-(phenyl methyl thio)-3-pyridine carboxylic acid disclosed in the prior art differ from each other with respect to the different chemical processes employed, use of the different basic raw materials, solvents and further differ in terms of the experimental parameters.
European Patent Numbered EP 0,547,035 to Hanagan Mary ann, discloses a process for preparing 2-(phenyl methyl thio)-3-pyridine carboxylic acid. The disclosed process comprises of making solution of 2-mercapto nicotinic acid, water sodium hydroxide and benzyl chloride, refluxing the solution, diluting with water, acidifying it by adding 36% HCl to get title compound.
Another U.S. Pat. No. 4,767,766 to Baker, et al., discloses the process for the preparation of 2-(phenyl methyl thio)-3-pyridine carboxylic acid comprising making solution of 2-mercapto nicotinic acid, methanol, sodium methoxide and benzyl bromide, stirring the solution, diluting with water, and acidifying the solution till pH 7 with glacial acetic acid to get desired product.
Although the yield of the product by the process mentioned in the prior art are satisfactory, the process is not economically viable because the major raw material 2-mercapto nicotinic acid itself is a high value intermediate.
2-(Phenyl methyl thio)-3-pyridine carboxylic acid is also prepared by reacting 2-chloro nicotinic acid with benzyl mercaptan in presence of a base and an aprotic solvent. Here again, the yield of the desired product is unsatisfactory and hence the process is not economically viable.
The known process suffers from a variety of disadvantages including the fact that during the course of the synthesis of 2-(Phenyl methyl thio)-3-pyridine carboxylic acid, certain impurities like benzyl alcohol is present when benzyl halide is used which is very difficult to isolate from the final product which add to more unwanted step for purification of intermediates and make the process more costly and time consuming. This is extremely disadvantageous in large scale productions of the title compound
Therefore, there is a need for an improved process for producing 2-(Phenyl methyl thio)-3-pyridine carboxylic acid especially suitable for large scale manufacture. Large scale manufacturing requires the production of the compound in a cost effective manner.
The invention disclosed herein demonstrates economically viable selective synthesis of intermediate 2-(Phenyl methyl thio)-3-cyano pyridine to manufacture the 2-(Phenyl methyl thio)-3-pyridine carboxylic acid using selective raw materials and appropriate experimental parameters, allowing the process to become industrial friendly for commercial scale and also better yield with high purity.